High modulus silicones as toughening agents for epoxy resins

ABSTRACT

This invention relates to certain new high modulus silicones, toughened epoxy thermoset resin systems made from those silicones, and composites that are prepared from the new toughened epoxy resin systems. The silicone resins are specifically monophenyl-containing polysiloxanes.

BACKGROUND OF THE INVENTION

This invention relates to certain new high modulus silicones, toughenedepoxy thermoset resin systems made from those silicones, and compositesthat are prepared from the new toughened epoxy resin systems.

Epoxy resins, one of the most widely used engineering resins arewell-known for their use in composites which utilize high strengthfibers. Articles can be manufactured from epoxy resins which are lighterin weight than the same articles manufactured from metals yet retainequivalent strength and stiffness. To date, epoxy composites have beenrelatively brittle due to the brittleness of the matrix resin. Thisbrittleness restricts the wider application of certain compositesbecause of the obvious problems associated therewith.

This problem has been attacked in a variety of ways, for example, Rowe,E. H. and Siebert, A. R., Mod. Plast. 47, 110 (1970 and McGarry, F. J.,Proc. Roy. Soc. Lond. A., 319, 59 (1970) have used linearpolybutadiene-polyacrylonitrile copolymers to toughen epoxy resins. Suchan approach works to toughen the laminates from such modified epoxyresins, but there is a drastic loss of hot-wet properties.

Jabloner, et al., in U.S. Pat. No. 4,656,207, issued on Apr. 7, 1987,discloses the use of amino terminated polysulfones to toughen epoxyresins. These polysulfones are much more effective toughening agentsthan polybutadiene-polyacrylonitrile copolymers. These polysulfones alsoincrease the toughness of the laminates made from the epoxy resins.However, these polysulfones must be used at high levels, at least fortyweight percent or more, so that the viscosity of mixed epoxy resins isincreased.

Organofunctional polysiloxanes have been used in combination with epoxyresins, but not in the toughening sense. For example, Hirose, et al, inEuropean Patent Publication 0 293,733 A2 disclose a curable polymercomposition. More particularly, they disclose a curable compositioncomprising an epoxy resin and an organic elastomeric polymer having inthe molecule, at least one silicon-containing group which iscrosslinkable through formation of a siloxane bond through asilicon-containing reactive group. This material is easily formulatedinto a one pack type composition and curable even at room temperatureand affords a cured product having improved mechanical properties suchas toughness and strength. Thus, they have provided a copolymer, whichis elastomeric in nature, and is not indicated as being useful fortoughening epoxy resins in composite applications.

In other polysiloxane combinations with epoxy resins, Yorkgitis andcoworkers, Yorkitis, E. M.; Tran, C.; Eiss, Jr., N. S.; Hu, T. Y.;Yilgor, I.; Wilkes, G. L. and McGrath, J. E.; "Siloxane Modifiers forEpoxy Resins" in Adv. Chem. Ser. 208 (Rubber Modified Thermoset Resins)137 to 161, (1984), have used essentially linear aminoalkyl endblockedrandom copolymers of diphenyl-dimethyl-siloxanes and random copolymersof methyltrifluoropropyl-dimethylsiloxanes to toughen epoxy resins.These materials have been found by Yorkgitis et al to toughen about aseffectively as the commercial polybutadiene-polyacrylonitrile copolymersdescribed supra, but these materials also cause a drastic loss ofhot-wet properties of the composite.

Yorkgitis et al have correctly stated that "A toughened material, bydefinition, features improvements in fracture resistance withoutsubstantial loss of mechanical strength or modulus." Yorkgitis et althen illustrate that the above-mentioned oligomeric polysiloxanes onlyslightly influenced the flexural modulus of the base epoxy resin,stating "As expected, the flexural modulus does decrease as rubbercontent increases. The decrease is less severe as either TFP(trifluoropropylmethylpolysiloxane) or DP (dimethylpolysiloxane) contentincreases."

From what is disclosed in the prior art, it thus appears thatessentially linear or essentially elastomeric organofunctionalpolysiloxanes are known, but they have not been used effectively totoughen epoxy resins for use in composite applications.

Therefore, it was unexpected that hard, brittle organofunctionalsilicone resins would toughen a hard, glassy, brittle, thermoset epoxyresin. In other words, the inventors herein believe that this is thefirst disclosure of the use of a hard brittle organopolysiloxane resinto toughen a hard brittle epoxy resin.

SUMMARY OF THE INVENTION

It is therefore an objective of this invention to provide novelphenyl-containing and aminofunctional-containing siloxane resins. It isa further objective to provide blended silicone-epoxy compositions thatare useful in preparing composite structures having increased fracturetoughness over epoxy resins not containing the novel silicones of thisinventions, while retaining essentially all of the mechanical andhot-wet properties of the original, untoughened epoxy resin.

The composites prepared using the blended silicone-epoxy resins of thisinvention have, in addition, thermostability for high temperatureapplications and, the ability to provide low water pickup by the curedcomposites.

This invention therefore comprises a toughened epoxy resin system,certain organofunctional polysiloxanes useful in toughening the epoxyresin system, and composites made from such toughened epoxy resinsystems.

In one aspect therefore, this invention comprises a composition ofmatter comprising a blend of (A) a curable epoxy resin, or a mixture ofcurable epoxy resins, and (B) an amino functional silicone resincomprising the units (i) PhSiO_(3/2) (ii) R₂ SiO and (iii)aminofunctional siloxy radicals selected from the group consistingessentially of a. H₂ NR^(i) SiO_(3/2), b. R^(iv) HNR^(ii) SiO_(3/2), c.(R^(iv) HNR^(ii))_(3-y) (R^(v))_(y) SiO_(1/2), d. (H₂ NR^(ii))_(3-x)(R^(v))_(x) SiO_(1/2) and, e. mixtures of a, b, c, and d, wherein Ph isthe phenyl radical; each R is independently selected from phenyl andalkyl groups of 1 to 3 carbon atoms with the provisio that when R is analkyl radical in each case, there can be no more than 10 weight percentof (ii) in the silicone resin and with the further provisio that whenone R is an alkyl radical and one R is a phenyl radical on the samesilicon atom, there can be no more than 15 weight percent of (ii)present in the silicone resin; R^(i) is a divalent hydrocarbon radicalselected from alkylene, arylene, alkarylene, and aralkylene having 1 to10 carbon atoms, and --R^(ii) NHR^(iii) --, wherein R^(ii) and R^(iii)are each independently selected from alkylene, arylene, alkarylene andaralkylene of 1 to 10 carbon atoms; each of x and y have a value of 0,1, or 2; R^(iv) is selected from methyl, ethyl, propyl or phenyl; R^(v)is selected from methyl and phenyl, and the aminofunctional siliconeresin has an --NH-- equivalent in the range of 350 to 1000.

Another aspect of this invention are the novel hard, brittle, resinousorganofunctionalpolysiloxanes (amino functional silicone resins) thatprovide the toughening of the epoxy resins comprising an aminofunctional silicone resin comprising the units (i) PhSiO_(3/2) (ii) R₂SiO and (iii) aminofunctional siloxy radicals selected from the groupconsisting essentially of a. H₂ NR^(i) SiO_(3/2), b. R^(iv) HNR^(ii)SiO_(3/2), c. (R^(iv) HNR^(ii))_(3-y) (R^(v))_(y) SiO_(1/2), d. (H₂NR^(ii))_(3-x) (R^(v))_(x) SiO_(1/2) and, e., mixtures of a, b, c, andd, wherein Ph is the phenyl radical; each R is independently selectedfrom phenyl and alkyl groups of 1 to 3 carbon atoms with the provisiothat when R is an alkyl radical in each case, there can be no more than10 weight percent of (ii) in the silicone resin and with the furtherprovisio that when one R is an alkyl radical and one R is a phenylradical on the same silicon atom, there can be no more than 15 weightpercent of (ii) present in the silicone resin; R^(i) is a divalenthydrocarbon radical selected from alkylene, arylene, alkarylene, andaralkylene having 1 to 10 carbon atoms, and --R^(ii) NHR^(iii) --,wherein R^(ii) and R^(iii) are each independently selected fromalkylene, arylene, alkarylene and aralkylene of 1 to 10 carbon atoms;each of x and y have a value of 0, 1, or 2; R^(iv) is selected frommethyl, ethyl, propyl or phenyl; R^(v) is selected from methyl andphenyl, and the aminofunctional silicone resin has an --NH-- equivalentin the range of 350 to 1000.

Yet another aspect of this invention is a composite that is preparedfrom the toughened epoxy resins of this invention, the inventioncomprising (I) a cured epoxy resin, or a mixture of cured epoxy resins,containing therein an amino functional silicone resin comprising theunits (i) PhSiO_(3/2), (ii) R₂ SiO and (iii) aminofuctional siloxyradicals selected from the group consisting essentially of a. H₂ NR^(i)SiO_(3/2), b. R^(iv) HNR^(ii) SiO_(3/2), c. (R^(iv) HNR^(ii))_(3-y)(R^(v))_(y) SiO_(1/2), d. (H₂ NR^(ii))_(3-x) (R^(v))_(x) SiO_(1/2) and,e. mixtures of a, b, c, and d, wherein Ph is the phenyl radical; each Ris independently selected from phenyl and alkyl groups of 1 to 3 carbonatoms with the provisio that when R is an alkyl radical in each case,there can be no more than 10 weight percent of (ii) in the siliconeresin and with the further provisio that when one R is an alkyl radicaland one R is a phenyl radical on the same silicon atom, there can be nomore than 15 weight percent of (ii) present in the silicone resin; R^(i)is a divalent hydrocarbon radical selected from alkylene, arylene,alkarylene, and aralkylene having 1 to 10 carbon atoms, and --R^(ii)NHR^(iii) --, wherein R^(ii) and R^(iii) are each independently selectedfrom alkylene, arylene, alkarylene and aralkylene of 1 to 10 carbonatoms; each of x and y have a value of 0, 1, or 2; R^(iv) is selectedfrom methyl, ethyl, propyl or phenyl; R^(v) is selected from methyl andphenyl, and the aminofunctional silicone resin has an --NH-- equivalentin the range of 350 to 1000, said composite having, (II) reinforcingfibers embedded therein prior to cure.

A final aspect of this invention is a process of preparing cured,reinforced, toughened epoxy resin-containing laminates, said processcomprising (I) blending an aminofunctional silicone resin with at leastone curable epoxy resin, at least one epoxy hardener; (II) impregnatingreinforcing fibers with said blend; (III) laying up at least two layersof the impregnated fibers to form a laminate; (IV) heating the laminateat a temperature sufficient and for a length of time sufficient to curethe epoxy resin, whereby a cured, reinforced, toughened epoxyresin-containing composite is obtained.

DETAILED EXPLANATION OF THE INVENTION

For purposes of this invention, the novel organofunctional polysiloxanesthat are contemplated within the scope of this invention are those thatare compatible or readily dispersible with the epoxy resin and thecuring agent for the epoxy resin. Further, the inventors herein considerthat silicone resins which are readily dispersible in the epoxy resin togive a homogeneous and uniform dispersion are also within the scope ofthis invention. This compatibility/dispersibility requirement pertainsto the silicone modified epoxy resin in the uncured state. Thosesiloxane resins that are not compatible or readily dispersible with theepoxy resin and its curing agent in the uncured state are not consideredto be within the scope of the invention claimed herein. However, it mustbe understood that the silicone resins useful herein are those that mustseparate and form a separate phase in the epoxy resin and curing agent,as the cure of the epoxy resin takes place.

The separation phenomena is dependent on the N--H equivalent of thepolysiloxane resin, the composition of the polysilicone resin, and thecomposition of the epoxy resin being used, along with its curing agent.

Certain aminofunctional organopolysiloxanes are known in the prior art.For example, there is disclosed in British patent 942,587, thepreparation of aminofunctional resins similar to those disclosed andclaimed in this invention that were found useful in modifying varnishesand lacquers. Some of the polysiloxane resins from the British patenthave amine equivalents that fall near those described for thepolysiloxane resins of the instant invention, but none of thepolysiloxane resins of the British Patent form part of the polysiloxaneresins of the instant invention, as their amine equivalents do not fallin the critical ranges described for the polysiloxanes resins of theinstant invention. Thus, as can be observed, none of the resins of thereference are those claimed in the instant invention.

Therefore, the aminofunctional silicone resins that are useful in theinstant invention comprise the units (i) PhSiO_(3/2) ; (ii) R₂ SiO, and(iii) aminofunctional siloxy radicals selected from the group consistingessentially of a. H₂ NR^(i) SiO_(3/2), b. R^(iv) HNR^(ii) SiO_(3/2), c.(R^(iv) HNR^(ii))_(3-y) (R_(v))_(y) SiO_(1/2), d. (H₂ NR^(ii))_(3-x)(R^(v))_(x) SiO_(1/2) and, e. mixtures of a, b, c, and d, wherein Ph isthe phenyl radical; each R is independently selected from phenyl andalkyl groups of 1 to 3 carbon atoms with the provisio that when R is analkyl radical in each case, there can be no more than 10 weight percentof (ii) in the silicone resin and with the further provisio that whenone R is an alkyl radical and one R is a phenyl radical on the samesilicon atom, there can be no more than 15 weight percent of (ii)present in the silicone resin; R^(i) is a divalent hydrocarbon radicalselected from alkylene, arylene, alkarylene, and aralkylene having 1 to10 carbon atoms, and --R^(ii) NHR^(iii) --, wherein R^(ii) and R^(iii)are each independently selected from alkylene, arylene, alkarylene andaralkylene of 1 to 10 carbon atoms; each of x and y have a value of 0,1, or 2; R^(iv) is selected from methyl, ethyl, propyl or phenyl; R^(v)is selected from methyl and phenyl, and the aminofunctional siliconeresin has an --NH-- equivalent in the range of 350 to 1000.

Thus, the aminofunctional silicone resin units R₂ SiO can be selectedsuch that R is independently selected from phenyl, and alkyl groups of 1to 3 carbon atoms such as, for example, units comprising dimethylsiloxy,phenylmethylsiloxy, diphenylsiloxy, methylpropylsiloxy andphenylpropylsiloxy, and the like. For purposes of this invention, when Ris an alkyl radical in each case, there can be no more than 10 weightpercent of this type of siloxy unit in the silicone resin, and further,when one R is an alkyl radical and one R is a phenyl radical on the samesilicon atom, there can be no more than 15 weight percent of this typeof siloxy unit present in the silicone resin.

R^(i) for purposes of this invention is a divalent hydrocarbon radicalselected from alkylene, arylene, alkarylene, and aralkylene having 1 to10 carbon atoms, and --R^(ii) NHR^(iii) --, wherein R^(ii) and R^(iii)are each independently selected from alkylene, arylene, alkarylene andaralkylene of 1 to 10 carbon atoms. Thus, the preferred R^(i) for thisinvention has from 2 to 8 carbon atoms, and most preferred is a divalentradical having three carbon atoms. R^(i) is also most preferred to bethree carbon atoms. R^(iii) is preferably the methyl or phenyl radicalwith methyl being the most preferred. R^(iv) is selected from methyl,ethyl, propyl or phenyl and R^(v) is selected from methyl and phenyl,with methyl being preferred in both cases.

The amount of amine in the silicone resin that is required to achievethe properties of the cured epoxy resin in this invention is an amountthat has an --NH-- equivalent in the range of 350 to 1000. Morepreferred are silicone resins having an --NH-- equivalent in the rangeof 400 to 900, and most preferred are those silicone resins having an--NH--equivalent in the range of 500 to 800.

Further, the amount of aminofunctional silicone resin that can be usedvaries depending on the component siloxy units. Typically, the siliconeresin can be used in amounts ranging from 5 weight percent to 30 weightpercent of the blend of silicone resin and epoxy resin. The amount ofthe silicone resin to use can be determined by the initial solubility ordispersibility of the silicone resin in the uncured epoxy resin. It isknown by the inventors herein that when the silicone resin contains(CH₃)₂ SiO units, only up to about 10% of the silicone resin can be usedin the blend. Further, it is known by the inventors herein that when(Ph)(CH₃)SiO units are used, the silicone resin can be used in the blendin up to 20 weight percent. It is further known by the inventors hereinthat certain materials of this invention, i.e., those having nodiphenylsiloxy units work only in certain epoxy resin systems. A simplesolubility test to help determine if the silicone resin is useful inthis invention is described in the prem ble to the examples.

The epoxy thermoset resins and the composites of this invention can beobtained from a thermosetting epoxy resin composition (A) comprising (a)at least one polyepoxy component having a glass transition temperaturebelow about 50° C. and (b) at least one epoxy hardener.

It is not uncommon to blend reactive epoxy resins to optimize physicaland other properties and the inventors herein contemplate such a use inthis invention.

The polyepoxy components contain at least 2 epoxy groups and preferablyare aromatic polyepoxy compounds having between 2 and about 4 epoxygroups per molecule and glass transition temperatures below 50° C.Suitable polyepoxy compounds are resorcinol diglycidyl ether{1,3-bis-(2,3-epoxypropoxy)benzene} marketed, for example, by WilmingtonChemical as HELOXY^(R) 69; diglycidyl ether of bisphenol A{2,2-bis(p-{2,3-epoxypropoxy}phenyl)propane}; triglycidylp-aminophenol{4-(2,3-epoxypropoxy)-N,N-bis{2,3-epoxypropyl)aniline};diglycidyl ether of bromobisphenol A{2,2-bis(4-{2,3-epoxypropoxy)3-bromo-phenyl)propane; diglydicylether ofBisphenol F (2,2-bis(p-(2,3-epoxypropoxy)phenyl)methane); triglycidylether of meta and/or para-aminophenol(3-(2,3-epoxypropoxy)N,N-bis(2,3-epoxypropyl)aniline); and tetraglycidylmethylene dianiline (N,N,N',N'-tetra(2,3-epoxypropyl)4,4'-diaminodiphenyl methane) or mixtures of two or more polyepoxycompounds can be used in this invention. A more exhaustive list of theepoxy resins found useful in this invention can be found in Lee, H. andNeville, K., Handbook of Epoxy Resins, McGraw-Hill Book Company, 1982reissue.

Another embodiment of this invention is the use of an aromatic oligomerand therefore, the epoxy thermoset resins and the composites of thisinvention can be obtained from a thermosetting epoxy resin composition(A) comprising (a) at least one polyepoxy component having a glasstransition temperature below about 50° C.; (b) at least one epoxyhardener; (c) at least one aromatic oligomer that is reactive with (a)or (b), or (a) and (b), and which has a molecular weight (numberaverage) between about 2000 and 10,000 and a glass transitiontemperature between about 120° C. and 250° C.

The aromatic oligomers, contain functional groups which are reactivewith the polyepoxy components and/or the epoxy hardeners of thecomposition. In a preferred embodiment the oligomer is epoxy reactiveand has at least about 1.4 epoxy reactive groups per molecule. Thereactive aromatic oligomer preferably contains divalent aromatic groupssuch as phenylene, diphenylene or napthalene groups linked by the sameor different divalent non-aromatic linking groups. Such linking groupsare for example, oxygen, sulfonyl, oxyalkylene or oxyalkyleneoxy such as--OR-- or --ORO-- wherein R is lower alkylene preferably with 1 to 3carbon atoms; lower alkylene or alkylidene such as --R-- or --R(R¹)_(y)-- wherein R and R¹ are independently lower alkylene and y is 1 or 2;ester groups such as --(R¹)_(x) COO(R²)y-- where R¹ and R² areindependently lower alkylene preferably with 1 to 3 carbon atoms and xand y are independently zero or 1; and oxoalkylene-(R¹)COR²)_(y) --,wherein R.sup. 1 and R² are independently lower alkylene where x and yare independently zero or 1. The aromatic units may be substituted withnon-interfering substitutents such as chlorine, lower alkyl, phenyl andthe like. Generally, at least twenty-five percent of the total number ofcarbon atoms in the reactive aromatic oligomer will be in aromaticstructures, and preferably at least about 50% of the total carbon atomsare in aromatic structures.

The preferred reactive aromatic oligomers comprise polyethers and morepreferably polyethers having two different types of units. A portion,preferably greater than half of these units, are aromatic.

Also preferred, are aromatic or cycloaliphatic units that are notbridged, for example, napthalene, or are bridged by groups which areessentially nonpolar, examples of which are alkylidene, such asisopropylidene bridges.

The reactive aromatic oligomers preferably have reactive groups that areterminal groups on the oligomer backbone and more preferably arereactive groups at the ends of oligomeric backbones which have little orno branching. The preferred reactive groups of the reactive aromaticoligomer are primary amine, hydroxyl, carboxyl, anhydride, thio,secondary amine and epoxy. Especially preferred are reactive aromaticoligomers having at least about 1.7 reactive groups per molecule andhaving at least about seventy percent of the total number of reactivegroups present as primary amine groups.

The epoxy hardner can be any compound with an active group capable ofreacting with the epoxy group. Preferably, it can be selected fromcompounds with amino, acid, anhydride or azide group. More preferablythe epoxy hardener is an aromatic diamine such as adiaminodiphenyl-sulfone; a methylenedianiline such as4,4'-methylenedi-aniline; a diaminodiphenylether; benzidine;4,4'-thiodi-aniline; 4-methoxy-6-m-phenylenediamine;2,6-diaminopyridine; 2,4-toluenediamine; and dianisidine. Alicyclicamines such as menthane diamine and heterocyclic amines such as pyridinemay also be employed. In some cases, aliphatic amines such as secondaryalkylamines which are normally fast reacting hardeners can be used aloneor in combination with other epoxy hardeners provided the concentrationand/or curing temperature are sufficiently low to permit control of thecuring rate. Other fast reacting hardeners which can be employed formaking the epoxy resins of the invention are dicyandiamide and borontrifluoride.

Other ingredients and adjuvants such as catalysts, modifiers, and thelike can be present provided their presence and amount does not destroythe advantages of the invention.

The epoxy resins and the composites of this invention can be producedconventionally, the only alteration in such a practice is theintroduction of the siloxanes of this invention to the epoxy resinsbefore they are cured.

Curing of the epoxy resins containing the siloxane of this inventionusually requires a temperature of at least about 40° C., and up to about200° C. for periods of minutes up to hours. Post Treatments can be usedas well, such post treatments ordinarily being at temperatures betweenabout 100° C. and 200° C. Preferably, curing is staged to preventexotherms, staging preferably commencing at temperatures below about180° C.

The epoxy resin matrices of this invention are particularly useful incomposites containing high strength filaments or fibers such as carbon(graphite), glass, boron and the like. Composites containing from about30% to about 70%, more preferably about 40% to 70%, of these fibersbased on the total volume of the composite are preferred in makingcomposite structures.

A preferred manner of making the prepregs is by hot melt prepregging.The prepregging method is characterized by impregnating bands or fabricsof continuous fiber with the thermosetting epoxy resin and siliconeresin composition in molten form to yield a prepreg which is layed upand cured, to provide a composite of fiber and thermoset resincontaining the siloxane.

Generally, for hot melt processing it is preferred to select apolyepoxide component having a Tg below 50° C. and an aminofunctionalsilicone resin which provide a mixed epoxy resin having a viscosity ofbetween about 100 and 10,000 centipoise more preferably between 200 andabout 5,000 centipoise at 100° C. In hot melt prepregging thecombination of polyepoxy component, aminofunctional silicone resin andhardener preferably has a viscosity below 15,000 centipoises at 100° C.

Other processing techniques can be used to form composites containingthe epoxy resin thermosets of this invention. For example, filamentwinding, solvent prepregging and pultrusion are typical processingtechniques in which the uncured epoxy resin can be used. Moreover,fibers in the form of bundles can be coated with the uncured epoxy resincomposition, layed up as by filament winding and cured to form thecomposites of this invention.

The epoxy resin matrices and composites of this invention areparticularly useful as structures for the aerospace industry and ascircuit boards and the like for the electronics industry, as well as forthe formation of skis, ski poles, fishing rods, and other outdoor sportsequipment.

TESTING PROCEDURES PREPARATIO OF CASTINGS FOR TESTING

A solution of the material to be tested was poured into molds made fromtwo pieces of glass. Each of the pieces of glass were treated on thesurfaces which would contact the solution with Dow Corning^(R) 20, asilicone release coating. The glass mold consisted of two glass plates,having narrow strips of cured silicone rubber spacers about 2 to 3 mmthick on their interior surfaces around the outside perimeter, exceptfor one edge, to provide a spacer between the two glass pieces to allowa hollow into which the solution could be poured. The glass pieces wereabout 150 mm square to give a molded piece of about 22,500 mm square and2 to 3 mm thick. The glass molds were preheated at 110° C. before theresin was poured into them. At 110° C., the solution was poured into themold through the open edge using a funnel and up to the level of the topof the glass plates. The resulting castings were kept at 110° C. untilall of the air had escaped from the casting leaving a smooth surface,essentially free of air bubbles, against the glass. The temperature wasthen raised to 130° C. and kept at this temperature for 2 to 4 hours togel the epoxy resin. The castings were then cured by raising thetemperature to 180° C. at a rate of 0.208° C./minute. The temperaturewas kept at 180° C. for 2 hours and then cooled to room temperature at arate of 1.3° C./minute.

MEASUREMENT OF FRACTURE TOUGHNESS (G_(1c))

The cured modified epoxy resins were tested by the method as essentiallytaught in Lee, S. M., "Double Torsion Fracture Toughness Test ForEvaluating Transverse Cracking in Composites", Journal of MaterialsScience Letters 1 (1982) 511 to 515. Three mm thick composite sampleswere cut into two pieces 60×120 mm. A wide scratch is made from thenotch down the center of the sample with a plastic cutter. Then a deepercut was made in the scratch with a razor carpet knife. The Fracturetoughness, G_(1c), of the sample was measured with an Instron Model 1122using the apparatus as shown essentially in Lee, supra. The sample isplaced on the holder with the cut side down and the edges on top of thestainless steel rods. The notch is placed between the stainless steelballs. Pressure is applied to the sample until it cracks. The crossheadis stopped as soon as the sample cracks and the force (P,Kg force)required to crack the sample, the distance the crosshead moved (d, mm)and the length of the crack (a, mm) are measured. The crosshead speedused was 1 mm/min. The crosshead was activated again and the process wascontinued until the sample broke. G_(1c) is calculated using thefollowing equation:

    G.sub.1c =(P.sup.2 /2t)(dC/da){Kgf(mm)/MM.sup.2 }

where t=thickness at the part of the crack extension and C is thecompliance. The compliance C is obtained by dividing the distance (d)the crosshead moves by P. The value of dC/da is obtained from the slopeof a plot of C versus a. G_(1c) is measured for each crack. The firstvalue in each case was discarded because abnormally high force isrequired to make the first crack. The average of the G_(1c) values ofthe remaining cracks is then reported as the G_(1c) of the sample. TheG_(1c) values reported herein are usually an average of four samples.

FLEXURAL MODULUS TESTING

Flexural Modulus on the samples was carried out by using Dow CorningCorporate Test Method No. 0491A entitled "Flexural Strength-Rigid andSemirigid Plastics". It is based on ASTM Test D 790 and uses a BaldwinUniversal Test Machine. The 1984 version has a reference number ASTM790-84A and is entitled "Flexural Properties of Unreinforced andReinforced Plastics and Electrical Insulating Materials". The resultsare reported in kg/mm². The silicone materials of the instant inventionprovide toughening of the epoxy resins while essentially not decreasingthe flexural modulus of the toughened epoxy resin. The materials usefulin this invention should not decrease the flexural modulus of the curedresin by more than about 11 percent.

WATER ABSORPTION TESTING

Water absorption tests were conducted on the samples by taking thepieces from the flexural modulus test that were approximately 2 mmthick, weighing them to get a base weight and then wrapping them incheese cloth to suspend them in boiling water. Periodically each samplewas removed, wiped dry and weighed. The percent weight increase from aninitially dry sample to the weight of the removed, wiped dry sample arereported as "% increase".

EXAMPLE 1 Preparation of Non-Aminofunctional Siloxane Resins

Non-aminofunctional silicone resins which do not fall within the scopeof this invention, were also tested in order to compare them to theaminofunctional silicone resins to determine if non-aminofunctionalresins would provide the appropriate properties in the composite inconjunction with the epoxy resins and also to show the superiority ofthe resins of the instant invention. The resins used are typicalsilicone resins that do not contain any amine functionality. They wereprepared by the well-known method of hydrolysis of chlorosilanes as setforth in Eaborn, C., "Organosilicon Compounds", Butterworths ScientificPublications London 1960 pp. 227 et seq.

OS-1 had a high phenyl content and consisted of 40 mol % phenylsiloxyunits, 45 mol % methylsiloxy units, 10 mol % diphenylsiloxy units, and 5mol % phenylmethylsiloxy units.

OS-2 consisted of 70 mol % phenylsiloxy units and 30 mol % propylsiloxyunits.

For convenience, the OS resin compositions are set forth in table formon Table I.

OS-1 and OS-2 were each tested in a curable epoxy resin system. Epon828, curable by DDS was treated with 30 weight % of OS-1 and OS-2 inseparate samples, respectively, using toluene solutions of the siliconeresins. The toluene was removed by heating the solutions in a 150° C.oil bath. Castings were attempted. With OS-2, the silicone precipitatedas gel particles after the DDS was dissolved and this mixture was notcast. OS-1 gave a clear solution and was cast. During the cure, thesilicone phase separated, but settled to the bottom of the castinginstead of forming a uniform dispersion throughout the casting. Neithermaterial toughens cured epoxy resins because of the exhibited behaviouras shown below.

    ______________________________________                                        COMPATIBILITY                                                                 SILICONE       MY 720   EPON 828                                              ______________________________________                                        OS-1           insoluble                                                                              soluble                                               OS-2           disperses                                                                              soluble                                               ______________________________________                                    

                  TABLE I                                                         ______________________________________                                        Non-Aminofunctional Silicone Resins                                           SILICONE      COMPONENTS   (mol %)                                            ______________________________________                                        OS-1          *PhSiO.sub.3/2                                                                             40                                                               CH.sub.3 SiO.sub.3/2                                                                       45                                                               Ph.sub.2 SiO 10                                                               PhCH.sub.3 SiO                                                                              5                                                 OS-2          PhSiO.sub.3/2                                                                              70                                                               PrSiO.sub.3/2                                                                              30                                                 ______________________________________                                         *Ph is Phenyl and Pr is Propyl                                           

Preparation of Aminofunctional Silicone Resins

An example of the preparation of aminofunctional silicone resinscomprises adding 5.7 mols (1128.6 g) of phenyltrimethoxysilane to xylene(1500 g) in a 5-liter round-bottomed, glass flask equipped with an airoperated stirrer, water cooled reflux condenser, an addition funnel anda thermometer. This mixture was heated to 70° C. and a solution of conc.HCl (2 ml., 0.0893 mol) in water (500 ml) was slowly added to themixture. CAUTIOUS ADDITION of the acidic water was undertaken to avoidpotential violent exothermic reactions which is attributable to thesolubility of water in the xylene owing to the presence of by-producedmethanol from the hydrolysis that takes place. After all of the acidicwater was added, the reaction was heated at reflux for one hour. Thereaction mass was cooled to below 60° C. and then there was added to theexisting reaction mass, KOH (20.96 g, 0.374 mol),octaphenylcyclotetrasiloxane (212 g, 1.07 eq) andaminopropyltrimethoxysilane (179 g, 1.0 mol). A Dean-Stark azeotropetrap was then attached to the condenser and the mixture heated toreflux. Water was azeotroped from the mixture. The methanol caused poorseparation of the organic and aqueous phases and considerable xyleneremained with the aqueous phase. Additional xylene (1000 ml) was addedto replace the xylene lost with the water. After all of the water hadbeen removed, the reaction was heated at reflux overnight (about 16hrs.). Acetic acid (23.58 g, 0.374 mole) was then added to the reactionmass. Upon cooling to room temperature, the reaction appeared cloudywhereupon it was filtered using nitrogen pressure. The filtrate waspoured into baking dishes and the xylene was allowed to evaporate in ahood. Residual xylene was removed in a vacuum oven at 5 Torr and about100° C. A white appearing, glassy material was obtained. This materialwas weak and friable.

Gel Permeation Chromatography analysis indicated it to be a resin havingan average molecular weight of about 1790. In determining the abovemolecular weight, a sample of the material was treated with aceticanhydride to convert the existing amine functionality of the sample toamide, to prevent the amine from being absorbed onto the packing in theGel Permeation columns. In this manner, the molecular weight values ofthe material are not skewed. A sample was then dissolved in toluene andtitrated with perchloric acid in acetic acid using methyl violetindicator to give an amine equivalent of 1088. This value converts to anamine-hydrogen (--NH--) equivalent of 544 because there are two aminehydrogens per nitrogen atom. This material is hereinafter designated asNH-1.

NH-2 was prepared identically to NH-1 except that the quantity ofoctaphenylcyclotetrasiloxane was doubled while the other reagents werekept the same.

NH-3 was a resin containing 36/55/8 weight percent of phenylsiloxyunits/diphenylsiloxy units/aminopropylsiloxy units at 60% solids inxylene wherein the precursor phenyltrimethoxysilane was hydrolyzed with250 ml of water and 2 ml of concentrated hydrochloric acid, using aprocedure similar to the preparation of NH-1.

NH-4 was prepared as in NH-1 except that the diphenyl units werereplaced with dimethyl units.

NH-5 was prepared as in NH-1 except that the diphenyl units werereplaced with phenylmethyl units.

NH-6 was prepared as in NH-1, except that the amount of theaminofunctional silane used was doubled. Also, 2000 ml of xylene wasused initially instead of 1500 to accomodate the xylene that was lostduring the azeotroping of the water that was formed by the reaction. Thequantities of water, hydrocloric acid, potassium hydroxide and aceticacid used were identical to that used above.

NH-7 was prepared without any phenyltrimethoxysilane, that is, the finalresin did not have any PhSiO_(3/2) units in it. Three hundred thirtythree grams of xylene were used to give 60% solids. No hydrochloric acidwas used. The potassium hydroxide (0.6 g, 0.011 mol) was dissolved in 20to 30 ml of water. The excess water was azeotroped from the reactionmixture and the reaction mass was heated at reflux overnight. Additionalsolvents, toluene (250 ml) and THF (250 ml) were used to reduce theviscosity of the solution so it would filter more easily. Afterfiltering the mixture, the solvent was allowed to evaporate from thefiltrate. The amine equivalent was calculated initially to be close tothat of NH-1.

NH-8 was prepared as in NH-1 except that the amount of amine was halved.

For convenience, the composition and properties of these resins are setforth on Table II.

                  TABLE II                                                        ______________________________________                                        AMINO-   FINAL RESIN                                                          FUNCT.   COMPOSITION*                Mol.                                     SILOXANE phenyl  diphenyl aminoalkyl     wt.                                  NO.      siloxy  siloxy   siloxy  NH (eq)                                                                              (Mw)                                 ______________________________________                                        NH-1     69.6    20.0     10.4    544    1790                                 NH-2     53.3    30.7     16.0    356    5160                                 NH-3     36.1    55.4     8.5     672     740                                 NH-4     79.3    8.7      12.0    519    --                                   NH-5     74.1    14.5     11.2    570    --                                   NH-6     63.0    18.2     18.8    .sup. 338.sup.1                                                                      2700                                 NH-7     00.0.sup.2                                                                            90.1     9.9     672    1000                                 NH-8     80.9    13.3     5.8     1035.sup.3                                                                           --                                   ______________________________________                                         *IN WEIGHT PERCENT                                                            SAMPLES NH6 through 8 are not within the scope of this invention.             1 the NH- equivalent is too low.                                              2 the resin does not contain PhSiO.sub.3/2.                                   3 the NH-equivalent is too high.                                         

Epoxy Resin Preparation

This method was used for essentially all of the epoxy resin examplesshown in this specification and is at least one method by which curableepoxy resins can be prepared.

Araldite MY 720, a curable epoxy resin manufactured by Ciba-Geigy,having an epoxy equivalent weight of 124 (253.4 g, 2.01 epoxyequivalents), and 4,4'-diaminodiphenyl-sulfone(hereinafter DDSmanufactured by the Aldrich Chemical Company, an epoxy resin hardenerhaving an amine equivalent of 62 (124.8 g, 2.01 NH equivalents) weremixed in a 900 ml Freeze Dry Flask. The mixture was heated in a 150° C.oil bath until a clear solution was obtained. This material, having nosilicone resin toughening agent was used as a control for plain epoxyresins and was designated Control-1.

One other curable epoxy resin used in these examples was Epon 828,manufactured by the Shell Chemical Company, having an epoxy equivalentof 191. This was Control-2.

Amino-Terminated Polysulfone Preparation

The amino-terminated polysulfone which is not within the scope of thisinvention, was compared herein against the materials of the instantinvention and was prepared following the directions of Jabloner, et. alas set forth in Part A of the examples of the patent. The amineequivalent was 2820 and the Gel Permeation Chromatography analysisshowed a molecular weight (Mw) of 5850 and (Mn) of 3770. The analysesagree quite closely with those of the Jabloner reference. This materialwas designated "polysulfone" and was tested for water absorptionproperties. (see FIG. 3).

Jabloner et al teach that the polysulfone must comprise 40 weight % ormore of the final resin composition. At 40 weight %, the polysulfone inMY 720/DDS gelled. At 20 weight % in MY 720/DDS, a good casting wasobtained but testing did not give valid G_(1c) results, because the testresults were erratic.

Simple Test for Compatibility of Siloxane Resins with the Epoxy Resins

A silicone resin (0.5 g) was dissolved in toluene (5 ml) and the epoxyresin is added at the desired level. The resulting solution or mixturewas placed in a 150° C. oil bath and the toluene allowed to evaporate.Compatibility of the siloxane with the epoxy resin was noted after allof the toluene had evaporated. If the resins are compatible, or thesilicone resin is uniformly dispersed in the epoxy resin, after thetoluene has evaporated, then the system is probably workable within thelimitations of the invention described herein, provided the othercritical limitations of this invention are met.

EXAMPLE 2 Preparation of Epoxy Resin Toughened with Silicone Resin

Araldite MY 720 (150 g., 1.19 equiva.) and NH-1 (56.1 g, 0.1 equiv.)were placed in a 900 ml Freeze Dry Flask. Toluene (300 ml) was added andthe mixture stirred at room temperature until clear in appearance. Theflask was heated in a 150° C. oil bath for about 30 minutes. The toluenewas allowed to evaporate during this time. Residual toluene was removedunder reduced pressure. The flask was cooled to about 80° C., and thenDDS (67.6 g, 1.09 eq.) was added and the mixture was stirred with aspatula until a smooth, homogeneous paste was obtained. The flask wasput back into the oil bath until all of the DDS had dissolved, which wasabout 30 minute. This mixture did not become crystal clear but remainedvery slightly transluscent.

The results can be found on Tables III and IV.

                                      TABLE III                                   __________________________________________________________________________    RESULTS OF TESTING OF THE SILICONE TOUGHENED                                  EPOXY RESIN COMPOSITES USING MY 720 AS THE                                    EPOXY RESIN AND DDS AS THE HARDENER                                                                       Flexural                                          SAMPLE                                                                              SILICONE                                                                              %      G.sub.1c                                                                          %.sup.!                                                                          Modulus                                                                             %                                           NUMBER                                                                              ADDITIVE                                                                              ADDITIVE                                                                             (N/m.sup.2)                                                                       INC.                                                                             (Kg/mm.sup.2)                                                                       LOSS                                        __________________________________________________________________________    *1    NONE     0      88 -- 374   --                                           2    NH-1     5     108 23 371   <1.0                                         3    NH-1    10     127 44 354   5.6                                          4    NH-1    10     147 67 NM                                                 5    NH-1    15     157 78 369   1.0                                          6    NH-1    20     216 145                                                                              348   7.4                                          7    NH-2    10     118 34 347   7.3                                          8    NH-2    15     127 44 345   7.2                                          9    NH-3    20     118 34 337   10.9                                        10    NH-4    20     127 44 377   NM                                          11    NH-5    20     154 75 NM                                                12    NH-6     5      59    348                                               13    NH-6    10      88    372   <1.0                                        14    NH-7    20     108 22 316   18.3                                        15    NH-8    10     (precipitated)                                           16    HYCAR CTBN                                                                            10     147 67 248   51                                          __________________________________________________________________________     .sup.! % Inc. = % increase                                                    NM = not measured                                                             *control                                                                 

                                      TABLE IV                                    __________________________________________________________________________    RESULTS OF TESTING OF THE SILICONE TOUGHENED                                  EPOXY RESIN COMPOSITES USING EPON 828 AS THE                                  EPOXY RESIN AND DDS AS THE HARDENER                                                                      Flexural                                           SAMPLE                                                                              SILICONE                                                                             %      G.sub.1c                                                                          %  Modulus                                                                             %                                            NUMBER                                                                              ADDITIVE                                                                             ADDITIVE                                                                             (N/m.sup.2)                                                                       INC.                                                                             (Kg/mm.sup.2)                                                                       LOSS                                         __________________________________________________________________________    **1   NONE    0     205 -- 325   --                                           2     NH-1   30     265 29 305   6.6.sup.+                                    3     NH-1   30     343 67 312   4.2.sup.++                                   __________________________________________________________________________     *CONTROL                                                                      .sup.+ the powdered DDS was hard to disperse in the silicone/epoxy            mixture.                                                                      .sup.++ the powdered DDS was added as an acetone solution.               

EXAMPLE 3

NH-1 was compared against a commercial organic material for its abilityto toughen epoxy resins. The commercial material was CTBN (carboxyterminated butadiene/acrylonitrile copolymer as described supra in thespecification.

Each material was solublized in hot, uncured MY 720 and DDS and eachsolution was cast into a glass mold as described above. After curing,the silicone containing material was translucent, indicating that thephase separation required in this invention had occurred. The CTBNsample was clear.

The amine functional silicone increased the fracture toughness by 2.5fold over a cured epoxy control containing no silicone or CTBN, withless than 10% loss of flexural modulus. At 10 Weight %, the aminefunctional silicone and the CTBN gave comparable toughening, but at 20Weight %, the silicone increased the G_(1c) by 2.5 fold. In addition,the CTBN causes an unacceptable loss of flexural modulus while thesilicone does not.

EXAMPLE 4 Preparation of A Unidirectional Prepreg

A unidirectional prepreg composed of the following was prepared.

A. reinforcing fibers: Carbon fibers T300 made by Toray Industries,Inc., Japan.

B. Matrix resin: A resin composition composed of the following:

1) Bisphenol A type epoxy resin, Epikote 834 made by Yuka Shell EpoxyK.K.

2) Phenol novolac type epoxy resin, Epicron N-740 made by Dainippon Ink& Chemicals, Inc.

3) Dicyan diamide made by Japan Carbide.

4) 3-(3,4-dichlorophenyl)-1,1-dimethylurea made by Dupont, Wilmington,Del.

5) NH-1 aminofunctional siloxane resin as described above.

The materials were used in the following amounts:

    ______________________________________                                        COMPONENT         AMOUNT (in parts)                                           ______________________________________                                        1                 64.0                                                        2                 35.0                                                        3                  3.5                                                        4                  4.0                                                        5                 11.8 (10 weight %)                                          ______________________________________                                    

The resin content in the prepreg was 35%. The amount of resins per unitarea was 78 g/m² and the amount of carbon fibers per unit area was 145g/m². Composite laminates were laid up and were cured at 130° C. for 2hours in an autoclave. Laminate tensile properties were determined usingspecimens as defined in ASTM D3039 and laminate compressive strengthswere determined using specimens as defined in ASTM D695.

Double cantilever beam specimens ({0}26, 33.02×1.27 cm) were used tomeasure mode I critical strain energy release rate G_(1c). Teflon stripswere inserted into the laminates at their midplanes to control crackinitiation. Open angle during tests were kept below 15° in order toavoid large displacement effects. Crosshead speed was 2.5 mm/min. Theresults are shown below.

                                      TABLE V                                     __________________________________________________________________________                           0° TENSILE                                                                    0° COMPRESSIVE                           SILICONE                                                                             %      G.sub.1c STRENGTH                                                                             STRENGTH                                        ADDITIVE                                                                             ADDITIVE                                                                             (Kgf · mm/mm.sup.2)                                                           (Kgf/mm.sup.2)                                                                       (Kgf/mm.sup.2)                                  __________________________________________________________________________    none    0     0.0136   163    163                                             NH-1   10     0.0192   165    162                                             __________________________________________________________________________

EXAMPLE 5

A material of this invention, NH-1 was tested for water adsorptionabilities.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the amount of water adsorbed by an epoxy resin system, MY720/DDS, with various levels of NH-1.

FIG. 2 shows the water absorption of NH-1 using the untreated MY 720/DDSepoxy resin as a control.

FIG. 3 shows the water absorption of NH-1 compared against polysulfoneand using the untreated epoxy resin as a control.

FIG. 4 shows the water absorption of NH-1 using the untreated Epon828/DDS epoxy resin as a control.

That which is claimed is:
 1. A composition of matter comprising a blendof(A) a curable epoxy resin, or a mixture of curable epoxy resins, and(B) an amino functional silicone resin comprising the units(i)PhSiO_(3/2) (ii) R₂ SiO and (iii) aminofunctional siloxy units selectedfrom the group consisting essentially of:a H² NR^(i) SiO_(3/2), b R^(iv)HNR^(ii) SiO_(3/2), c (R^(iv) HNR^(ii))_(3-y) (R^(v))_(y) SiO_(1/2), d(H₂ NR^(ii))_(3-x) (R^(v))_(x) SiO_(1/2) and, e mixtures of a, b, c, andd,wherein Ph is the phenyl radical; each R is independently selectedfrom phenyl or alkyl groups of 1 to 3 carbon atoms with the provisiothat when R in B(ii) is an alkyl radical in each case, there can be nomore than 10 weight percent of B(ii) in the silicone resin and with thefurther provisio that when one R in B(ii) is an alkyl radical and one Rin B(ii) is a phenyl radical on the same silicon atom, there can be nomore than 15 weight percent of (ii) present in the silicone resin; R^(i)is a divalent hydrocarbon radical selected from alkylene, arylene,alkarylene, or aralkylene having 1 to 10 carbon atoms, and -R^(ii)NHR^(iii) -, wherein R^(ii) and R^(iii) are each independently selectedfrom alkylene, arylene, alkarylene or aralkylene of 1 to 10 carbonatoms; each of x and y have a value of 0, 1, or 2; R^(iv) is selectedfrom methyl, ethyl, propyl or phenyl; R^(v) is selected from methyl orphenyl, and the aminofunctional silicone resin has an --NH-- equivalentin the range of 350 to 1000.